1. Field of the Invention
The present invention relates to resin molded articles and a production method therefor.
2. Description of the Related Art
In recent years, resin molded articles are used for many members and parts constituting industrial products. The resin molded articles are composed of various resin materials solely or in combination, and are molded into a required shape depending on a required function, performance, property, etc. For example, various kinds of resin molded articles have been used as functional members such as containers, casing, lids, spool cores and cassette cases, for accommodating, wrapping, covering, protecting, transporting, storing, shape retaining or otherwise handling recording materials such as photographic recording materials, magnetic recording materials and optical recording materials. For example, resin molded articles made from various resin materials are used as the functional members for accommodating the body of a recording material, such as cassettes, magazines, and film cases with lenses. The resin molded articles are also used for containers for simply protecting recording materials; housing cases for audiocassette tapes and videotapes; and holding cases for CD, MD, etc.
Few of the resin molded articles are permanently stored, but most of them will be disposed or will be classified and subjected to regeneration treatment if they are reusable, when the industrial products in which the resin molded articles have been incorporated, finish their role, or after the resin molded articles themselves have performed their function. For example, the resin molded articles such as various members or components that constitute the above-mentioned recording materials will be separated and discarded at the time of use or during use of the recording materials, or discarded together with the recording materials to be discarded.
However, conventional resin molded articles are difficult to be decomposed when they are disposed of in the natural environment. This is one of the factors that contaminate the environment.
Accordingly, in recent years, the uses of the materials that are decomposed under the natural environment have been studied. Biodegradable resins, which are known as resin materials decomposed under the natural environment, are inferior in heat resistance to the conventional plastics, so that they are deformed under conditions where the temperature increases to as high as that in a car in summer seasons and none of them can exert the function thereof. For example, it has become possible to mass-produce poly lactic acid originated from corn starch as a raw material at low cost. The poly lactic acid has attracted attention as a biodegradable resin that is friendly to the terrestrial environment since it is reusable to enable making effective use of resources and since even if it is discarded, it will be decomposed under natural environment and give no adverse influence to the environment.
However, the poly lactic acid shows considerable softening at above 60° C., since it has a low glass transition temperature of as low as 58° C., so that they are deformed under environmental conditions of high temperature, for example, as that in a car in summer seasons and thus it is difficult to utilize it for applications where heat resistance is required. Therefore, there has been a demand for the development of a technology that can utilize biodegradable resins such as poly lactic acid in molded articles of which heat resistance is required.